DIRECT AB-INITIO DYNAMICS CALCULATIONS OF THERMAL RATE CONSTANTS AND KINETIC ISOTOPE EFFECTS FOR THE H--]OH+H-2 REACTION(H2O[)

We present an application of our previously proposed direct ab initio dynamics method for calculating the thermal rate constants and kinetic isotope effects (KIEs) of the H + H2O <-- --> OH + H-2 reaction. Dyna mical calculations were based on a full canonical variational transiti on-state theory plus multidimensional semiclassical tunneling correcti ons. The minimum energy path (MEP) and Hessians at selected points alo ng this path were calculated at the QCISD/6-311+G(d,p) level of theory . The classical potential energy along the MEP was further improved by a series of single-point PMP4/6-311++G(2df,2pd) calculations. The pre dicted rate constants and KIEs are in excellent agreement with experim ental data for the temperature range from 250 to 2000 K. The accuracy of the Schatz-Elgersma analytical potential energy function for this r eaction has also been examined.